1. Field of the Invention
The present invention generally relates to diesel fuel. More particularly, the invention relates to a diesel fuel (or biodiesel fuel) additive composition comprising certain organo-nitrates and/or nitro-organic compounds with cyclic diene and/or cyclic triene that thermally decompose under high temperature to generate highly reactive radicals. When these compounds are combined in a fixed range of concentrations, significant performance and fuel economy benefits in a diesel engine are produced.
2. Description of the Related Art
In a diesel-fueled engine, the single-most limiting parameter is poor air utilization. The fuel is sprayed into the combustion chamber as a liquid stream when the piston is very close to top dead center, leaving very little time for atomization and mixing. Fuel will only burn when atomized and mixed with air, so the liquid fuel in the core of the spray begins to pyrolyze and form solid matter. Greater amounts of particulate matter are produced at higher loads, where relatively large amounts of fuel need to be atomized in less than a millisecond. Additionally, as more time is consumed to atomize the fuel, the production of NOx increases.
Engine manufacturers currently address this problem by installing very high pressure fuel injection equipment to assist in atomization. However, the pumping loss directly attributable to this high pressure injection robs 10% to 15% of the engine's energy output. Engine manufacturers also presently rely heavily on exhaust gas recirculation (EGR) to control NOx emissions. EGR, however, lowers the bulk gas temperature, lowers work output and causes combustion instability. The use of biodiesel further stresses the efficient execution of combustion due to its lower volatility and the high oxygen content of the fuel (>10% more oxygen content when compared with traditional diesel fuel). Moreover, the gums and deposits that the biodiesel tends to build on the injectors and in the combustion chamber itself compromise the combustion process.
Detergent fuel additives are well known as capable of restoring lost fuel economy and reducing exhaust emissions by removing deposits on injector nozzles and in the combustion chamber. Even so, these fuel additives cannot improve combustion beyond a clean engine. Metallic based fuel additives are also well-known combustion enhancing additives and can improve performance and reduce particulate matter formation in a diesel engine. However, these metal based additives are known to poison catalysts and have harmful effects on humans and the environment.
An improved way of quickly dispersing the liquid fuel spray and atomizing the fuel is desirable. There remains a need for a fuel additive technology which significantly enhances engine efficiency and reduces harmful exhaust emissions without imposing harmful side effects.
Applicant's prior U.S. Pat. No. 8,470,058 attempts to address this problem and teaches that a diesel fuel additive with a formulation of at least 75% 1-methyl-4 (1-methylethenyl)-cyclohexene and the remainder a cetane improver will yield measurable fuel economy benefits in medium and heavy duty diesel engines. This discovery was based upon combustion bomb tests that demonstrate an earlier pressure build in the combustion event and on-the-road heavy duty truck tests. The disclosure describes the most likely mechanism of action as early start of combustion resulting from enhanced atomization and mixing of the diesel fuel with the bulk air charge by the thermal cracking of 1-methyl-4 (1-methylethenyl)-cyclohexene along with the addition of a cetane improver to off-set the atomization of low cetane components. A concentration of cetane improver higher than 25% was shown in combustion bomb tests and road tests to diminish the benefit of the formulation. It was also well known that higher amounts of cetane improver adversely affect NOx.